The purpose of this project is to analyze functional properties of a novel cytoplasmic domain isoform of beta1 integrin, beta1D, that displaces the beta1A isoform in striated muscles. The major hypothesis is that beta1D integrin provides an enhanced cytoskeletal-matrix association and displays distinct signaling properties in muscle cells. The effect of beta1D integrin transfection into nonmuscle cells, on cell morphology, adhesion, spreading, contractility, cell migration and extracellular matrix assembly will be determined. Muscle cytoskeletal protein(s) interacting with beta1D integrin will be identified by coimmunoprecipitation and affinity chromatography on immobilized beta1D and beta1A cytoplasmic domain peptides or fusion proteins containing the cytoplasmic tails of beta1D and beta1A. Detected interactions of known cytoskeletal protein(s) with the cytoplasmic domain of beta1D will be studied further in vitro by solid phase binding assays with purified cytoskeletal protein(s). Antibodies will be generated against novel cytoskeletal and/or signaling protein(s) interacting with beta1D integrin in muscle cells. Signaling properties of beta1D and beta1A integrin isoforms in muscle cells, such as integrin-mediated tyrosine phosphorylation, activation of pp125 FAK, pp6 src and other protein kinases, will be studied using separated myoblasts and myotubes and adhesion of myotubes specifically via transfected human beta1D or beta1A integrin. Inhibition of beta1D synthesis in differentiating muscle cells by expression of inducible beta1D-specific antisense transcript will define the role of beta1D integrin in myodifferentiation, including myotube growth, sarcomere assembly and muscle contraction. The effect of exogenous beta1D expression on cell cycle progression in myoblasts and normal or oncogene-transformed fibroblasts will be determined. Elucidating the role of beta1D integrin in muscle cells will help to understand how these cells differentiate and fulfill their functions under normal and pathological conditions.